The invention relates generally to semiconductor devices, and more particularly, to an apparatus and method for performing diffusion on a device such as a spherical-shaped semiconductor diode.
Conventional integrated circuits, or xe2x80x9cchips,xe2x80x9d are formed from a flat surface semiconductor wafer. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several layers are processed onto the semiconductor wafer surface. Once completed, the wafer is then cut into one or more chips and assembled into packages. Although the processed chip includes several layers fabricated thereon, the chip still remains relatively flat.
Manufacturing the wafers requires creating rod-form polycrystalline semiconductor material; precisely cutting ingots from the semiconductor rods; cleaning and drying the cut ingots; manufacturing a large single crystal from the ingots by melting them in a quartz crucible; grinding, etching, and cleaning the surface of the crystal; cutting, lapping and polishing wafers from the crystal; and heat processing the wafers. Moreover, the wafers produced by the above process typically have many defects. These defects can be attributed to the difficulty in making a single, highly pure crystal due to the cutting, grinding and cleaning processes as well as impurities associated with containers used in forming the crystals. These defects become more and more prevalent as the integrated circuits formed on these wafers contain smaller and smaller dimensions.
In U.S. Pat. No. 5,955,776, which is hereby incorporated by reference, a method and apparatus for manufacturing spherical-shaped semiconductor integrated circuit devices is disclosed. Although certain systems and methods for performing various processing operations are discussed in the above-referenced patent, it is desired to further improve on the operations. For example, in making a p-n junction diode, a first type (e.g. n-type) outer layer is diffused onto a second type (e.g., p-type) spherical shaped semiconductor substrate. It is desired that both the outer layer and the inner substrate are maintained at an appropriate shape, thickness, and diffusion concentration.
U.S. Pat. Ser. Nos. 09/490,650 and 09/489,782, which are hereby incorporated by reference, provide improved methods for doping material on a spherical shaped substrate in a non-contact environment. These methods can be used to make spherical p-n junction diodes for solar cell applications. It is desired, however, to make uniform sized spherical p-n diodes in a continuous operation (e.g., a single step).
The present invention, accordingly, provides a system and method for performing diffusion on a three-dimensional substrate. In one embodiment, the system includes a furnace for providing a doped (e.g., p-type) molten semiconductor material and a dropper for converting the molten semiconductor material into a series of uniformly sized-droplets. The droplets are then provided to a first tube where they solidify into semiconductor crystals.
The semiconductor crystals are then heated for a predetermined period of time until an outer layer of the semiconductor crystals is melted. The melted outer layer can be doped (e.g., n-type) using liquid state diffusion, and then allowed to re-solidify. As a result, a plurality of spherical shaped p-n devices is created.
In some embodiments, the semiconductor crystals are polished before they are melted. The polishing helps to remove deformities and better insure that the outer layer is of a desired thickness.
In some embodiments, the dropper utilizes a vibrating nozzle.
One embodiment of the method for making a p-n junction on a three-dimensional substrate includes forming a solid spherical shaped semiconductor crystal of a first dopant type. An outer layer of the spherical shaped semiconductor crystal is then melted to a predetermined thickness. A second dopant type can then be provided to the melted outer layer to be diffused into the outer layer. As a result, the doped and melted outer layer can be solidified to form the a p-n junction device.
Therefore, what is provided is an improved system and method for performing diffusion on a three-dimensional substrate. In the present example, the system and method can be used to make spherical shaped diodes with a uniform layer thickness in a single step operation.